Storage apparatus and data management method

ABSTRACT

Storage apparatus and data management methods provide for high-speed copying of a compressed data volume. A control unit of the storage apparatus divides a pool into a plurality of chunks including a plurality of pages storing data, compresses data which is written to a logical volume by a host, and assigns one of the plurality of chunks to a compressed data logical volume which stores the compressed data. When the compressed data logical volume is copied, the control unit makes a page length of the chunk assigned to the compressed data logical volume that is a copy source equivalent to a page length of the chunk assigned to the compressed data logical volume that is the copy destination.

TECHNICAL FIELD

The present invention relates to a storage apparatus and a datamanagement method and is suitably applied to a storage apparatus anddata management method with which data is compressed and stored.

BACKGROUND ART

As a system for storing large-scale data from a host, a storageapparatus which controls data I/Os from the host is used. The storageapparatus is an apparatus for managing, in a RAID (Redundant Array ofIndependent Inexpensive Disks), a multiplicity of drives arranged as anarray. At least one or more logical areas (hereinafter these areas mayalso be described as logical volumes) are formed in physical storageareas which are provided by the multiplicity of drives installed in thestorage apparatus and the logical volumes are provided to the host.

In order to store large-scale data from a host, a storage apparatusholds a large capacity storage area, but data from hosts has graduallyincreased over the years and there is a need for efficient storage oflarge-scale data due to problems relating to the size and cost of astorage apparatus.

Therefore, a reversible data compression system, which makes it possibleto reduce the amount of data and replace same with other small-size datawhile maintaining the amount of information of substantial quality inthe data, has been applied to a storage apparatus.

For example, PTL1 discloses a storage system with which data iscompressed and the optimum storage position is selected on the basis ofthe compressed data size.

CITATION LIST Patent Literature

PTL 1: Japanese Patent KOHYO Publication No. 2012-504795

SUMMARY OF INVENTION Technical Problem

Further, if an uncompressed data volume (uncompressed VOL) is compressedto generate a compressed data volume (compressed VOL), the usagecapacity of the storage area decreases. Hence, a shortening of the timefor copying the compressed VOL in comparison with an uncompressed VOL isto be expected. However, with the storage system of PTL1, the continuityof the data in the storage area cannot be guaranteed and high-speedcopying of the compressed VOL is sometimes impossible.

The present invention was conceived in view of the above points andproposes a storage apparatus and a data management method with whichhigh-speed copying of a compressed data volume is possible.

Solution to Problem

In order to achieve the foregoing object, the present invention proposesa storage apparatus which is coupled via a network to a host whichissues data I/O requests, comprising a storage unit which stores datawhich is read/written by the host, and a control unit which provides avirtualized logical volume to the host, manages a storage area which isprovided by the storage unit as a pool, and assigns a storage area ofthe pool to the logical volume on the basis of the data I/O requestsfrom the host, wherein the control unit divides the pool into aplurality of chunks comprising a plurality of pages storing data,wherein the control unit compresses data which is written to the logicalvolume by the host and assigns one of the plurality of chunks to acompressed data logical volume which stores the compressed data, andwherein, when the compressed data logical volume is copied, the controlunit makes the page length of the chunk which is assigned to thecompressed data logical volume which is the copy source the same as thepage length of the chunk which is assigned to the compressed datalogical volume which is the copy destination.

With this configuration, a storage apparatus is provided which providesa virtualized logical volume to the host, manages a storage area whichis provided by the storage unit as a pool, and assigns a storage area ofthe pool to the logical volume on the basis of the data I/O requestsfrom the host. The storage apparatus divides the pool into a pluralityof chunks comprising a plurality of pages storing data, compresses datawhich is written to the logical volume by the host and assigns one ofthe plurality of chunks to a compressed data logical volume which storesthe compressed data, and, when the compressed data logical volume iscopied, makes the page length of the chunk which is assigned to thecompressed data logical volume which is the copy source the same as thepage length of the chunk which is assigned to the compressed datalogical volume which is the copy destination. As a result, when thelogical volume which stores the compressed data is copied, high-speedcopying is possible without the need for random-access reading,compressed data expansion, or reconstruction of the compressed LUmapping table, and so forth.

Advantageous Effects of Invention

The present invention enables high-speed copying of a compressed datavolume.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a hardware configuration of a computersystem according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a managementterminal according to this embodiment.

FIG. 3 is a conceptual diagram showing an example of an LU managementscreen according to this embodiment.

FIG. 4 is a conceptual diagram illustrating initial compressionprocessing according to this embodiment.

FIG. 5 is a table showing the content of a compressed LU mapping tableaccording to this embodiment.

FIG. 6 is a conceptual diagram showing content of an unused areamanagement bitmap according to this embodiment.

FIG. 7 is a table showing content of a chunk management table accordingto this embodiment.

FIG. 8 is a flowchart showing an initial compression procedure accordingto this embodiment.

FIG. 9 is a conceptual diagram illustrating data read processingaccording to this embodiment.

FIG. 10 is a flowchart showing data read processing according to thisembodiment.

FIG. 11 is a conceptual diagram illustrating data write processingaccording to this embodiment.

FIG. 12A is a flowchart showing data write processing according to thisembodiment.

FIG. 12B is a flowchart showing compression processing according to thisembodiment.

FIG. 13 is a conceptual diagram illustrating compressed P-VOL copyprocessing according to this embodiment.

FIG. 14 is a flowchart showing compressed P-VOL copy processingaccording to this embodiment.

FIG. 15 is a conceptual diagram illustrating write processing in thecase of a paired state according to this embodiment.

FIG. 16A is a flowchart illustrating write processing in the case of apaired state according to this embodiment.

FIG. 16B is a flowchart showing compression processing in the case of apaired state according to this embodiment.

FIG. 17 is a conceptual diagram illustrating compressed data copyprocessing of the prior art.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described in detailhereinbelow with reference to the drawings.

(1) Computer System Configuration

FIG. 1 is a block diagram showing a hardware configuration of a computersystem according to a first embodiment of the present invention. Asshown in FIG. 1, a plurality of hosts 101 and a storage apparatus 110are coupled to a network 103 such as a SAN (Storage Area Network), forexample. Further, a management terminal 102 and a storage apparatus 110are coupled to a management network 104 such as a LAN (Local AreaNetwork), for example.

The host 101 is a computer which issues I/O requests (write requests orread requests) to the storage apparatus 110. The management terminal 102is a terminal for managing the storage apparatus 110.

(2) Storage Apparatus Configuration

The storage apparatus 110 comprises a controller 120 and a storagedevice group 112. The storage device group 112 is configured from aplurality of HDD 111. Note that, a physical storage device of anothertype, for example a flash memory device or the like, may also be adoptedinstead of the HDD 111.

The controller 120 receives an I/O request which is issued by the host101 and accesses any one or more of the HDD 111 in accordance with theprocessing of the I/O request. The controller 120 comprises a pluralityof host IF 121, a management IF 122, a CPU 123, a main memory 124, acache memory 125, an involatile memory 130, and an HDD IF 126. Further,these parts are all connected by an internal bus 127.

The host IF 121 is an interface circuit for communicating with anexternal device such as the host 101 via the SAN 103. The host IF 121receives I/O requests from the host 101. The management IF 122 is aninterface circuit for communicating with external devices such as themanagement terminal 102 via the management network 104. The HDD IF 126is an interface circuit for communicating with the HDD 111.

The cache memory 125 is a volatile memory, for example. The cache memory125 temporarily stores write target data corresponding to a writerequest received from the host 101 and read target data whichcorresponds to a read request received from the host 101.

The involatile memory 130 stores a management terminal communicationprogram 131, a pool management program 132, an I/O processing program133, an LU copy program 134, a compression/expansion program 135, acompressed LU mapping table 136, an unused area management bitmap 137,and a chunk management table 138. Computer programs which are stored inthe involatile memory 130 are loaded into the main memory 124 and theseprograms are executed by the CPU 124.

The management terminal communication program 131 is a program forcommunicating with the management terminal 102 (more specifically, astorage communication program 212 of the management terminal 102 whichwill be described subsequently). The pool management program 132 is aprogram for performing pool management-related processing such asvirtualization of a plurality of HDD. The I/O processing program 133 isa program for performing I/O-related processing such as reading andwriting of data from a pool. The LU copy program 134 is a program whichcopies LUs (Logical Units) which are data volumes in accordance withinstructions from the management terminal 102. The compression/expansionprogram 135 compresses or expands data elements which are input. Notethat, at least one of compression and expansion may also be realized bya hardware circuit. Various programs and various tables will bedescribed in detail subsequently. Further, in the following description,the processing which is performed by the computer programs is actuallycarried out by the CPU 123 which executes the computer programs.

(3) Management Terminal Configuration

FIG. 2 is a block diagram showing a configuration of the managementterminal 102.

The management terminal 102 is a computer and, as shown in FIG. 2,comprises an input device 201, an output device 202, a CPU 203, a mainmemory 204, a management IF 205, and an HDD 210, for example.

The input device 201 is a pointing device (a mouse, for example) and akeyboard and so on. Further, the output device 202 is a display device,for example.

The HDD 210 (may be a storage device of another type) stores a userinterface control program (hereinafter called an UI control program) 211and a storage communication program 212. These computer programs areloaded into the main memory 204 and the loaded programs are executed bythe CPU 203.

The management IF 205 is an interface circuit for communicating withexternal devices such as the storage apparatus 110 via the managementnetwork 104. The UI control program 211 is a program for displaying aGUI (Graphical User Interface) on the output device 202. The storagecommunication program 212 is a computer program for communicating withthe storage apparatus 110. The UI control program 211 and the storagecommunication program 212 will be described in detail subsequently.

FIG. 3 is a conceptual diagram showing an example of the LU managementscreen.

An LU management screen 301 is a GUI which is displayed by the UIcontrol program 212. The LU management screen 301 comprises an LU# (LUnumber) input field 302, an input field 303 for the capacity of the LU,and compression selection buttons 304 for selecting whether data storedin the LU is to be compressed. The user uses the input device 201 shownin FIG. 2 to input the number of the desired logical volume (LU number)in the LU# input field 302 and to input the LU capacity in the LUcapacity input field 303. In addition, the user selects and presses thecompression selection button 304 compression on or compression off.

When the OK button is pressed by the user, the storage communicationprogram 212 reports the LU number which has been input in the LU# inputfield 302, information indicating the capacity which is input in the LUcapacity input field 303, and information (compression on or compressionoff) which corresponds to the designated compression selection button304 to the storage apparatus 110. The management terminal communicationprogram 131 receives this information and the pool management program132 assigns a storage area which is used by the LU designated by theuser.

If, on the other hand, the user has already designated a generated LU#in the LU# input field 302, the LU capacity input field 303 may enter astate where inputs from the user are not accepted and the current LUusage amount may be displayed. In addition, the compression selectionbutton 304 may also be displayed in a state where the current selectionstate (compression on or compression off) is selected.

For example, suppose that the OK button is pressed in order to changethe selection of an LU in a compression off state to compression on. Inthis case, the storage communication program 212 reports the inputinformation to the storage apparatus 110. Further, when compression onis designated for the LU storing the uncompressed data, the storageapparatus 110 compresses the already stored uncompressed data and storesthe compressed data in the pool once again.

More specifically, the management terminal communication program 131receives the information from the management terminal 102 and the poolmanagement program 132 assigns a storage area for storing the compresseddata. The I/O processing program 133 reads the uncompressed data withthe designated LU number from the management terminal 102, generatescompressed data as a result of the compression/expansion program 135compressing the data, and the I/O processing program 133 stores thecompressed data in a compressed data storage area (compressed LU chunk)assigned by the pool management program 132. After repeatedly executingthe foregoing processing for all the uncompressed data, the area storingthe uncompressed data is then unused. It is therefore recognized by thepool management program 132 that the unused area is not being used andthe usage amount of the compressed data storage area is displayed as theLU usage amount which is displayed on the LU management screen 301.

Furthermore, suppose that the OK button is pressed in order to changethe selection of an LU in a compression on state to compression off. Inthis case, the storage communication program 212 reports the inputinformation to the storage apparatus 110. When compression off isdesignated for a compressed LU storing compressed data is designated,the storage apparatus 110 expands already stored compressed data andstores the expanded data in the pool once again.

More specifically, the management terminal communication program 131receives the information from the management terminal 102 and the poolmanagement program 132 assigns a storage area for storing uncompresseddata. The I/O processing program 133 reads the compressed data with thedesignated LU number from the management terminal 102, generatesuncompressed data as a result of the compression/expansion program 135expanding the data, and the I/O processing program 133 once again storesthis data in an uncompressed data storage area (an uncompressed LUchunk) assigned by the pool management program 132. After repeatedlyexecuting the foregoing processing for all the compressed data, the areastoring the compressed data is then unused. It is therefore recognizedby the pool management program 132 that the unused area is not beingused and the usage amount of the uncompressed data storage area isdisplayed as the LU usage amount which is displayed on the LU managementscreen 301.

(4) Overview of Compression Processing

FIG. 4 is a conceptual diagram illustrating initial compressionprocessing. More specifically, FIG. 4 shows an overview of initialcompression processing in the storage apparatus 110 in a case wherecompression on has been designated for an LU (uncompressed LU 401)storing uncompressed data via the LU management screen 301 in FIG. 3.

The uncompressed LU 401 is an LU in which uncompressed data is stored. Acompressed LU 402 is an LU in which uncompressed data stored in theuncompressed LU 401 is compressed and the compressed data is stored. TheLU numbers which identify the uncompressed LU 401 and the compressed LU402 may be the same or different LU numbers. That is, the fact that theuncompressed LU 401 and the compressed LU 402 have the same LU numbermeans that, once the initial compression processing is complete, the LUnumber of the uncompressed LU 401 is handed over to the compressed LU402. If, on the other hand, the uncompressed LU 401 and the compressedLU 402 have different LU numbers, the LU number of the compressed LU 402is designated by the management terminal 102.

The pool 403 is a pool area for storing real data which is written tothe uncompressed LU 401 and the compressed LU 402. The pool 403 may be aso-called thin provisioning volume to which capacity is dynamicallyassigned in small amounts at a time. Further, the pool 403 is used bybeing divided into a plurality of chunks. The page length is set foreach chunk and the I/O processing on the chunks is processed by takingthe page length as the smallest unit.

Uncompressed LU chunks 410 are areas for storing write data written tothe uncompressed LU 401. Write data for a plurality of uncompressed LU401 can also be stored in the uncompressed LU chunks 410.

Compressed LU chunks 411 are areas for storing write data written to thecompressed LU 402. Further, in a case where compression of theuncompressed LU 401 is instructed by the management terminal 102, [thecompressed LU chunks 411] are areas in which data which is stored in theuncompressed LU chunks 410 is compressed and the compressed data isstored. The compressed LU chunks 411 differ from the uncompressed LUchunks 410; only write data for one compressed LU 402 is stored in asingle compressed LU chunk 411, and write data of a plurality ofcompressed LU 402 is not stored. Thus, only data of one type ofcompressed LU is stored in a compressed LU chunk. As a result, when acompressed LU is copied, chunks can be copied sequentially, and hencethe speed required for copying can be improved.

For example, when compression on is designated for the uncompressed LU401 via the management terminal 102, the storage apparatus 110 readsuncompressed data from the uncompressed LU chunk 410 which stores realdata of the uncompressed LU 401 to the cache memory 125. The storageapparatus 110 then performs processing to compress the read uncompresseddata and stores the compressed data in the compressed LU chunk 411.Further, the storage apparatus 110 creates or updates various tables toenable access by the host 101 to the data in the compressed LU chunk 411from the compressed LU 402. More specifically, the storage apparatus 110creates and updates a compressed LU mapping table (illustrated in FIG. 5hereinbelow) which associates the logical address of the compressed LU402 with the storage address of the compressed LU chunk 411, and anunused area management bitmap (illustrated in FIG. 6 hereinbelow).Further, the storage apparatus 110 updates the chunk management table(illustrated in FIG. 7 hereinbelow).

(5) Content of Various Tables

FIG. 5 is a table showing the content of the compressed LU mappingtable. The compressed LU mapping table 136 is a table for managing thecorrespondence relationships between the logical address of thecompressed LU 402 and storage addresses of the compressed LU chunks 411.As shown in FIG. 5, the compressed LU mapping table 136 is configuredfrom a logical address field 1361, a compression flag field 1362, and astorage address field 1363.

The logical address field 1361 stores the logical addresses of thecompressed LU 402. The host 101 uses these logical addresses to requestI/O processing from the storage apparatus 110.

The compression flag field 1362 stores information indicating whether ornot the data is compressed. If data is not compressed, 0 is stored [inthis field], and if data is compressed, 1 is stored.

The storage address field 1363 stores offset addresses in the compressedLU chunks 411. Storing the offset addresses of the compressed LU chunk411 in the storage address field 1363 permits sharing of the compressedLU mapping table when copying the compressed LU 402, and hence theamount of memory consumption is curbed.

While the size of compression target data is of a fixed length, thecompressed data has a variable length. Therefore, an entry is added tothe logical address field 1361 in the table for each compression targetdata size of a fixed length. The units of the compression target datasizes may be the same as the page size of the uncompressed LU chunk 410or may be a multiple of the page size.

Meanwhile, entries are added to the storage address field 1363 in thetable in page size units of the compressed LU chunk 411. Therefore, ifthe compression target data size is 64 kB and the page size of thecompressed LU chunk 411 is 16 kB, for example, there is a single entryin the logical address field 1361 in the compressed LU mapping table136, while the storage address field 1363 holds four entries.

Further, since the compressed data is of a variable length, not all theinformation need be stored in the storage address field 1363. Forexample, the number of pages used in the compressed LU chunk 411 issmall in a case where the compression effect is large, and hence thereis also little information held in the storage address field 1363. NULLis held in an unused entry 510 of the storage address field 1363.

On the other hand, when the number of pages used in the compressed LUchunk 411 is large in a case where the compression effect is small, allthe information is stored in the storage address field 1363. As shown byentry 511 in FIG. 5, if there is no compression effect, data is writtento the compressed LU chunk 411 while still remaining uncompressed. Thecompression flag field 1362 stores information indicating whether thedata is uncompressed data or compressed data. It is possible todetermine whether data has been compressed by referencing thecompression flag field 1362.

FIG. 6 is a conceptual diagram showing the content of an unused areamanagement bitmap. One unused area management bitmap 137 exists for onecompressed LU chunk. The unused area management bitmap 137 is a bitmapin which page usage states in chunks are stored. As shown in FIG. 6, theunused area management bitmap stores 1 if a page is used and 0 if pagesare unused.

As shown in FIG. 4, in a case where initial compression from anuncompressed LU to a compressed LU is executed, because a compressed LUchunk 411 is newly secured, [data] is continuously stored in the orderof compression. Therefore, the unused area management bitmap 137 iscontinuously written from the start to 1 and, when the write processingto the compressed LU 402 is repeated, there is an increase or reductionin the data size after recompression due to updates to existing storeddata.

If the [data] size after recompression is large, 0 is detected from theunused area management bitmap 137, data corresponding to the increase isstored in the corresponding unused page, and the entry of the unusedarea management bitmap 137 is updated to 1. Furthermore, if the [data]size after recompression is small and an unused page is generated in thecompressed LU chunk 411, the entry of the unused area management bitmap137 corresponding to the unused page is updated from 1 to 0.

FIG. 7 is a table showing the content of a chunk management table. Thechunk management table 138 is a table for managing chunk-relatedinformation. The chunk management table 138 is configured from a chunknumber field 1381, a page size field 1382, an LU number field 1383, acompressed LU mapping table address field 1384, and an unused areamanagement bitmap address field 1385.

The chunk number field 1381 stores information representing target chunkidentifiers. The page size field 1382 stores the page sizes of thechunks. For example, in the case of the uncompressed LU chunk 410,information indicating 64 kB is stored in the page size field 1382 andin the case of the compressed LU chunk 411, information indicating 16 kBis stored in the page size field 1382.

The LU number field 1383 stores LU numbers which correspond to the datain the chunks. The LU number field 1383 is information which is addedonly in the case of a compressed LU chunk. In the case of anuncompressed LU chunk, because data for a plurality of LU is stored in asingle chunk, as mentioned earlier, a single LU is not specified for asingle chunk as it is for a compressed LU chunk. NULL, which indicates ablank field, is therefore stored as the LU number corresponding to theuncompressed LU chunk.

The compressed LU mapping table address field 1384 stores addresseswhere the compressed LU mapping table corresponding to the chunk isstored. Further, the unused area management bitmap address field 1385stores addresses where the unused area management bitmap 137corresponding to the chunk is stored. The compressed LU mapping tableaddress 1384 and the unused area management bitmap address 1385 areinformation which is added only if the chunk is a compressed LU chunk.This is because a compressed LU mapping table 136 and an unused areamanagement bitmap 137 which correspond to the uncompressed LU chunk donot exist.

(6) Details of Compression Processing

(6-1) Details of Initial Compression Processing

FIG. 8 is a flowchart showing an initial compression procedure in a casewhere compression of an uncompressed LU 401 is instructed by themanagement terminal 102.

First, the storage apparatus 110 receives the initial compressioninstruction from the management terminal 102 (S101). The pool managementprogram 132 of the storage apparatus 110 then determines whether or notthere is space in the compressed LU chunk (S102).

If it is determined in step S102 that there is no space in thecompressed LU chunk, the pool management program 132 secures acompressed LU chunk and updates the chunk management table 138 (S103).For example, directly after there is an initial compression instructionfrom the management terminal 102, there is a state where a compressed LUchunk has not been generated, and hence the pool management program 132secures a compressed LU chunk. Even when a compressed LU chunk has beenused up and there is no space in the compressed LU chunk, the poolmanagement program 132 secures a new compressed LU chunk. Further, if anew compressed LU chunk is secured, the pool management program 132 addsinformation on the secured chunk to the chunk management table 138.

If, on the other hand, at least the compression target data size can bestored in the compressed LU chunk, the pool management program 132executes the processing of step S104.

Further, the I/O processing program 133 of the storage apparatus 110reads at least the compression target data size from the start addressof the uncompressed LU to the cache memory 125 (S104).

The compression/expansion program 135 of the storage apparatus 110 thencompresses the uncompressed data in the cache memory 125 which was readin step S104 (S105). The compression/expansion program 135 thendetermines whether there is a compression effect from the data sizeafter the compression which is executed in step S105 (S106). If it isdetermined that there is a compression effect for the post-compressiondata, the compression/expansion program 135 executes the subsequentprocessing by taking the compressed data as a target. If, on the otherhand, it is determined that there is no compression effect, thecompression/expansion program 135 discards the compressed data andexecutes the subsequent processing by taking the uncompressed data as atarget.

Further, the pool management program 132 of the storage apparatus 110specifies the storage position in the compressed LU chunk from theunused area management bitmap 137 (S107). The pool management program132 then adds an entry for the data processed immediately before to thecompressed LU mapping table 136. Further, the pool management program132 updates the unused area management bitmap 137 (S108).

The I/O processing program 133 of the storage apparatus 110 then storesdata in the compressed LU chunk specified in step S107 (S109).

The pool management program 132 of the storage apparatus 110 thendetermines whether or not compression target data remains in theuncompressed LU (S110). If it is determined in step S110 thatcompression target data remains in the uncompressed LU, the poolmanagement program 132 repeats the processing of step S102 andsubsequent steps. If, on the other hand, it is determined in step S110that no compression target data remains in the uncompressed LU, the poolmanagement program 132 releases the uncompressed LU chunk if theuncompressed LU chunk can be released and deletes the entry for theuncompressed LU chunk from the chunk management table 138 (S111).

(6-2) Details of Read Processing

FIG. 9 is a conceptual diagram illustrating data read processing from acompressed LU. As shown in FIG. 9, the storage apparatus 110, whichreceives a read request of the compressed LU 402 from the host 101,references the compressed LU mapping table 136 (not shown) and reads thedata from the compressed LU chunk 411 to the cache memory 125. If thedata which is read from the cache memory 125 is compressed data, thestorage apparatus 110 executes expansion processing and transfers only areading range from the expanded data to the host 101.

FIG. 10 is a flowchart showing processing to read data from thecompressed LU 402. As shown in FIG. 10, the storage apparatus 110receives a read request from the host 101 (S201). The I/O processingprogram 133 of the storage apparatus 110 then performs a cache hit/missdetermination for the read data (uncompressed data) and determineswhether or not read data exists in the cache memory 125 (S202).

It a cache hit is determined in step S202, that is, if read data existsin the cache memory 125, the I/O processing program 133 executes theprocessing of step S206.

If, on the other hand, a cache miss is determined in step S202, that is,if it is determined that no read data exists in the cache memory 125,the I/O processing program 133 performs a cache hit/miss determinationfor the compressed data (S203). More specifically, the I/O processingprogram 133 references the compressed LU mapping table (not shown),acquires the storage address of the compressed data, and determineswhether or not there is compressed data at the corresponding cachememory address.

If a cache hit is determined in step S203, that is, if compressed datacorresponding to the read data exists in the cache memory 125, the I/Oprocessing program 133 executes the processing of step S205. If, on theother hand, a cache miss is determined in step S203, that is, ifcompressed data corresponding to the read data does not exist in thecache memory 125, the I/O processing program 133 references thecompressed LU mapping table and reads the data from the compressed LUchunk to the cache memory 125 (S204).

The compression/expansion program 135 then executes expansion processingif the data read in step S204 has been compressed (S205) but does notperform expansion processing if the data read in step S204 isuncompressed.

The I/O processing program 133 then specifies a reading range from theuncompressed data in the cache memory 125, transfers this range to thehost (S206), and ends the read processing.

(6-3) Details of Write Processing

FIG. 11 is a conceptual diagram illustrating processing to write data tothe compressed LU 402. As shown in FIG. 11, the storage apparatus 110which receives a request to write to the compressed LU 402 from the host101 immediately transfers write data to the cache memory 125. Thestorage apparatus 110 then transmits a status response signifying thatwrite processing is complete to the host 101.

The storage apparatus 110 starts compression processing asynchronouslyto the processing of the I/O from the host 101. The compressionprocessing is started when dirty data in the cache memory 125 (datawhich has not been written to the HDD) is equal to or greater than athreshold or when the CPU load is low (in cases where there are few I/Orequests from the host), and so on.

When the compression processing is started, the I/O processing program133 performs processing to supplement the compressed data. Compresseddata supplementation processing by the I/O processing program 133 isprocessing to keep the size of the compression target data at a fixedsize. If the uncompressed data is compressed, as mentioned earlier,although the compression is performed using compression target data sizeunits, there is no relationship between the write size from the host andthe compression target data size, and hence the write size may also beoverwritten if small in comparison with the compression target datasize. In order to make the overwrite data consistent with the existingstorage data, the I/O processing program 133 temporarily reads andexpands the compressed data which has been compressed and stored, andoverwrites same with expanded data only in the range written by thehost.

The I/O processing program 133 compresses uncompressed data whosecompression target data size has been curbed by the supplementationprocessing and stores the data once again in the compressed LU chunk411. At this time, the post-compression data will likely be increased orreduced relative to the size of the existing storage data. If thepost-compression data is greater than the existing storage data and thepage usage amount of the compressed LU chunk increases, the I/Oprocessing program 133 references the unused area management bitmap 137and secures an unused page. The I/O processing program 133 then storesthe corresponding increase in the compressed data in the secured pageand updates the page of the unused area management bitmap 137 to 1. TheI/O processing program 133 also updates the compressed LU mapping table136.

FIG. 12A is a flowchart showing processing to write data to thecompressed LU 402. As shown in FIG. 12A, the storage apparatus 110 firstreceives a write request from the host 101 (S301). The I/O processingprogram 133 then transfers the write data to the cache memory 125 (S302)and transmits a status response indicating completion of writing to thehost 101 (S303).

FIG. 12B is a flowchart showing compression processing. The storageapparatus 110 starts compression processing asynchronously to writeprocessing in response to an I/O request of the host 101. When thecompression processing is started, the compression/expansion program 135first determines whether or not there is compression target data in thecache memory 125 (S310). Compression target data signifies data (dirtydata) which has been transferred from the host 101 to the cache memory125 but which has not yet been written to the HDD 111.

If it is determined in step S310 that there is no compression targetdata, the compression/expansion program 135 ends the processing.

If it is determined in step S310 that there is compression target data,the compression/expansion program 135 executes compressed datasupplementation processing by means of read processing of the compressedLU chunk 411 (S311). The compressed data supplementation processing instep S311 is the same as the processing of steps S202 to S205(processing A) shown in FIG. 10. In other words, thecompression/expansion program 135 executes read processing from thecompressed LU chunk 411 and compressed data expansion processing forparts with an insufficient compression target data size which have anaddress close to the compression target data.

Further, the compression/expansion program 135 overwrites the data whichis expanded in step S311 with update data (S312).

The compression/expansion program 135 then recompresses the data whichis overwritten in step S312 and stores this data in the compressed LUchunk 411 (S313). The processing to write to the compressed LU chunk isthe same as the processing of steps S105 to S109 (processing B) in FIG.8. That is, the compression/expansion program 135 executes compressionprocessing and, depending on the case, references the unused areamanagement bitmap 137, specifies a storage area, and stores thecompressed data in the compressed LU chunk. Further, thecompression/expansion program 135 updates the compressed LU mappingtable 136 and the unused area management bitmap 137.

(7) Details of Copy Processing

LU copy processing will be described next. In the processing to copy anuncompressed LU, a copy instruction designating a copy source LU number(P-VOL) and a copy destination LU number (S-VOL (Secondary Volume)) istransmitted from the management terminal 102 to the storage apparatus110. The storage apparatus 110 which receives the copy instructionsequentially reads data from the start of the logical address of theP-VOL which is the copy source to the cache memory 125, copies the datato the S-VOL area in the cache, and stores the data in the storagedestination of the S-VOL which is the copy destination.

(7-1) Details of Conventional Copy Processing

Here, compressed data copy processing which is disclosed in PTL1 will bedescribed with reference to FIG. 17. FIG. 17 shows a conceptual diagramin a case where copying of an LU storing compressed data is executed bya conventional storage apparatus 1700. The compressed P-VOL 1701 showsthe copy-source LU. Further, the data which is stored in the compressedP-VOL 1701 is compressed data. The compressed S-VOL 1702 shows a copydestination LU. In a case where copying is performed from the compressedP-VOL 1701 to the compressed S-VOL 1702, the compressed data is storedin the compressed S-VOL 1702.

The compressed LU chunk 1703 is a chunk which stores compressed data. InPTL1, the data of two LU may be stored in the same chunk because theoptimum chunk is selected according to the post-compression data size.

Upon receiving a copy instruction designating the compressed P-VOL 1701and the compressed S-VOL 1702 from the management terminal 102, thestorage apparatus 1700 references the compressed LU mapping table (notshown) and reads the compressed data from the start of the logicaladdress of the compressed P-VOL 1701 to the cache memory 125. Thecompressed data is stored discretely in a plurality of chunks and hence,even if the data is read in the order of the logical address of thecompressed P-VOL 1701, physically, reading takes place using randomaccess.

In addition, because no mechanism for copying compressed data isprovided in PTL1, copying must be performed after expanding compresseddata which is read. It is also necessary to recompress the copied datato generate the storage data of the compressed S-VOL 1702. Further, thecompressed LU mapping table (not shown) must be reconstructed for use bythe compressed S-VOL.

As described earlier, when a copy of the compressed P-VOL 1701 is madeby the storage apparatus 1700 disclosed in PTL1, reading takes placeusing random access, and expansion processing and reconstruction of thecompressed LU mapping table, and so on, occur, and hence there is aproblem in that the copy time is longer than for an uncompressed LU eventhough the data has been compressed and the data size is small.Therefore, in this embodiment, the time for copying a compressed volumeis shortened by means of the copy processing shown below.

(7-2) Overview of Copy Processing of the Embodiment

FIG. 13 is a conceptual diagram illustrating copy processing of acompressed P-VOL according to the present invention. A compressed P-VOL1301 represents a copy source LU which stores compressed data. Thecompressed S-VOL 1302 represents a copy destination LU. If a copy ismade from the compressed P-VOL 1301 to the compressed S-VOL 1302,compressed data is stored in the compressed S-VOL 1302 in the same wayas for the compressed P-VOL. Note that, if copying is performed, thecompressed P-VOL 1301 and the compressed S-VOL 1302 are in a pairedstate and writing to the compressed S-VOL is prohibited. A compressedP-VOL chunk 1303 is a chunk which corresponds to the compressed P-VOL1301 and stores compressed data. The compressed S-VOL chunk 1304 is achunk which corresponds to the compressed S-VOL 1302. The same value isset for a page size 703 of the compressed P-VOL chunk 1303 and thecompressed S-VOL chunk 1304.

When a copy instruction designating the compressed P-VOL 1301 and thecompressed S-VOL 1302 is received from the management terminal 102, thestorage apparatus 110 starts the LU copy program 134.

The LU copy program 134 references the chunk management table 138 andacquires the chunk # (compressed P-VOL chunk 1303) storing compresseddata from the LU# which corresponds to the compressed P-VOL 1301.Thereafter, the LU copy program 134 reads to the cache memory 125 in theorder of the storage address of the compressed P-VOL chunk 1303 and notin the order of the logical address of the compressed P-VOL 1301.

The LU copy program 134 then copies the read compressed data to thecompressed S-VOL area as is without expanding the data and stores thedata in the compressed S-VOL chunk 1304. Thereupon, if there is a pagewhere no data is stored in the compressed P-VOL chunk 1303, the LU copyprogram 134 does not store data in the same way as the compressed P-VOLchunk 1303 on the same page of the compressed S-VOL chunk 1304.

Thus, sequential copying in the order of the address in the chunk can berealized by copying the compressed P-VOL chunk 1303 and the compressedS-VOL chunk 1304 in exactly the same state. Further, since copying isnot performed in the order of the logical address, there is no need toexpand the compressed data. As mentioned earlier, with this embodiment,high-speed copy processing can be realized.

(7-3) Details of Copy Processing

FIG. 14 is a flowchart showing copy processing of the compressed P-VOL1301. As shown in FIG. 14, the storage apparatus 110 first receives acopy instruction which contains information on the compressed P-VOL andthe compressed S-VOL from the management terminal 102 (S401).

Further, the LU copy program 134 references the chunk management table138 and determines whether the chunk exists from the LU numbercorresponding to the compressed P-VOL 1301 (S402). In the case of aninitial copy, if the designated LU number is not found in the chunkmanagement table 138, the LU copy program 134 notifies the managementterminal 102 that the LU number designation by the management terminal102 is incorrect and ends the processing.

If it is determined in step S402 that the designated LU number has beenfound in the chunk management table 138, the LU copy program 134 securesthe compressed S-VOL chunk 1304 which is the copy destination area(S403).

More specifically, the LU copy program 134 adds information of thecompressed S-VOL chunk 1304 to the chunk management table 138. The pagesize of the compressed S-VOL chunk 1304 is set at the same value as thecompressed P-VOL chunk 1303. Further, the values of the compressed LUmapping table address 705 and the unused area management bitmap address706 are configured with the same addresses as the informationcorresponding to the compressed P-VOL chunk 1303. As a result, becausethe data storage states of the compressed P-VOL 1301 and the compressedS-VOL 1302 can be the same state, sequential copy processing can beexecuted without further processing of the compressed data. There isalso no need to reconstruct the compressed LU mapping table 136 of thecompressed S-VOL 1302 and the compressed LU mapping table 136 of thecompressed P-VOL 1301 can be used for the compressed S-VOL 1302.

Further, the amount of memory used can be reduced because the compressedLU mapping table 136 and the unused area management bitmap 137 whichcorrespond to the compressed S-VOL 1302 are also common to thecompressed P-VOL 1301.

In addition, in a case where the paired state of the compressed P-VOLand the compressed S-VOL is released (split state), writing to thecompressed P-VOL and the compressed S-VOL is executed independently. Inthis case, the LU copy program 134 copies the compressed LU mappingtable 136 and the unused area management bitmap 137 which correspond tothe compressed S-VOL and updates the values of the compressed LU mappingtable address field 1384 and the unused area management bitmap addressfield 1385 of the chunk management table 138. As a result, writing tothe compressed S-VOL in the split state can also be executed normally.

Further, the LU copy program 134 references the chunk management table138, acquires the compressed P-VOL chunk 1303 storing the compressedP-VOL data, and reads the compressed data from the start of the chunk tothe cache memory 125 in the order of the storage addresses (S404).

The LU copy program 134 then copies the compressed data which is read instep S404 as is to the compressed S-VOL cache area (S405). The LU copyprogram 134 then stores compressed data, which has been copied to thecompressed S-VOL cache area, in the compressed S-VOL chunk 1304 (S406).Thereupon, the storage address of the compressed S-VOL chunk 1304 isconfigured with exactly the same offset as the compressed P-VOL chunk1303 (the offset address in the chunk).

Thereafter, the LU copy program 134 determines whether or not there isstill data to be copied to the compressed P-VOL chunk 1303 (S407). If itis determined in step S407 that there is data to be copied in thecompressed P-VOL chunk 1303, the LU copy program 134 repeats theprocessing of step S404 and subsequent processing. If, on the otherhand, copying of all the data in the compressed P-VOL chunk 1303 iscomplete, the LU copy program 134 updates the information of thecompressed S-VOL chunk 1304 of the chunk management table 138 (S408).

After executing the processing of step S408, the LU copy program returnsonce again to step S402 and references the chunk management table 138 todetermine whether or not the chunk exists from the LU numbercorresponding to the compressed P-VOL 1301. If it is determined in stepS402 that the chunk does not exist, the LU copy program determines thatall the copy processing is complete and ends the LU copy processing.

(8) Paired State Write Processing

The write processing in a case where the P-VOL and the S-VOL are in apaired state after the LU copy processing will be described next. If theP-VOL and the S-VOL are in a paired state after copy processing of anuncompressed LU, writing to the S-VOL is in many cases not allowed, butwhen writing to the P-VOL is performed, the same content is also writtento the S-VOL.

In the storage apparatus 110, write data which is received from the host101 is copied in the cache memory and this data is stored to each of thestorage destination disks P-VOL and S-VOL. In the foregoing PTL1, incases where a compressed P-VOL and a compressed S-VOL are in a pairedstate, write data is copied in the cache memory when write processing tothe P-VOL is performed. Therefore, compression processing is alsoexecuted for any write data in the P-VOL area and S-VOL area in thecache memory, and data is stored in each of the storage destinations. Inother words, there is a problem in that the compression processing isexecuted a total of two times and the processing load is large. In thisembodiment, as will be described hereinbelow, the processing load islightened by executing the compression processing only once.

FIG. 15 is a conceptual diagram illustrating write processing in a casewhere the compressed P-VOL 1301 and the compressed S-VOL 1302 are in apaired state according to this embodiment. First, when a write requestis issued from the host 101 to the compressed P-VOL 1301, write data istransferred to the cache memory 125. The storage apparatus 110 startscompression processing asynchronously to the write request from the hostI/O, performs processing to supplement the compression target data size,and executes compression processing.

Thereafter, the storage apparatus 110 copies the compressed data to theS-VOL area in the cache memory and stores the compressed data in thecompressed P-VOL chunk 1303 and the compressed S-VOL chunk 1304.According to this processing routine, compression processing can beexecuted once and copying to the compressed S-VOL 1302 can also beperformed normally.

FIGS. 16A and 16B are flowcharts showing write processing to, andcompression processing of, the compressed P-VOL 1301 in a case where thecompressed P-VOL 1301 and the compressed S-VOL 1302 are in a pairedstate.

As shown in FIG. 16A, the storage apparatus 110 receives a write requestto write to the compressed P-VOL 1301 from the host 101 (S501). The I/Oprocessing program 133 then transfers write data to the cache memory 125(S502).

The LU copy program 134 then copies the write data of the cache memory125 to the S-VOL area of the cache memory (S503). The data which is tobe copied to the compressed S-VOL 1302 is compressed data and thereforestep S503 can be omitted. However, when the paired state between thecompressed P-VOL 1301 and the compressed S-VOL 1302 is released, becauseI/Os are allowed from the host to the compressed S-VOL 1302, there isthe advantage that write data is copied to the S-VOL of the cache memoryand the cache hit rate improves.

Thereafter, the LU copy program 134 transmits a status responseindicating write completion to the host (S504).

Further, the storage apparatus 110 starts compression processingasynchronously to the I/O request from the host 101. The compressionprocessing is started, similarly to the foregoing compressionprocessing, in cases where the dirty data (data which has not beenwritten to the HDD) in the cache memory 125 is equal to or greater thana threshold or where the CPU load is low (there are few I/O requestsfrom the host), and so on.

As shown in FIG. 16B, when the compression processing is started, thecompression/expansion program 135 determines whether or not compressiontarget data is in the cache memory 125 (S510). Compression target datais data (dirty data) which has been transferred from the host 101 to thecache memory 125 but which has not yet been written to the HDD 111.

If it is determined in step S510 that there is no compression targetdata in the cache memory 125, the compression/expansion program 135 endsthe processing.

If, on the other hand, it is determined in step S510 that there iscompression target data in the cache memory 125, thecompression/expansion program 135 executes compressed datasupplementation processing by means of read processing of the compressedLU chunk 1303 (S511). The compressed data supplementation processing instep S511 is the same as the processing (processing A) of steps S202 toS205 in FIG. 10. In other words, the compression/expansion program 135executes read processing from the compressed LU chunk 411 and compresseddata expansion processing for parts with an insufficient compressiontarget data size which have an address close to the compression targetdata.

The compression/expansion program 135 then overwrites the data which isexpanded in step S1606 with update data (S512).

The compression/expansion program 135 then recompresses the data whichis overwritten in step S512 (S513). The compression processing of stepS513 is the same as steps S105 to S108 (processing C) in FIG. 8. Thatis, the compression/expansion program 135 executes compressionprocessing and, depending on the case, references the unused areamanagement bitmap 137 and specifies a storage area. Further, thecompression/expansion program 135 updates the compressed LU mappingtable 136 and the unused area management bitmap 137.

The compression/expansion program 135 then copies the compressed datawhich is compressed in step S513 to the S-VOL area of the cache memory125 (S514), and stores the compressed data in each of the compressedP-VOL chunk 1303 and the compressed S-VOL chunk 1304 (S515).

(9) Advantageous Effects of Embodiment

As described hereinabove, with this embodiment, the storage apparatus110 is provided in which the pool management program 132 of the storageapparatus 110 provides the virtualized logical volume 401 to the host101, manages the storage area provided by the HDD 111 as the pool 403,and, on the basis of a data I/O request from the host 101, assigns thestorage area of the pool 403 to the logical volume 401. The storageapparatus 110 divides the pool 403 into a plurality of chunks containinga plurality of pages storing data, compresses data which is written tothe logical volume 401 by the host 101, assigns one of a plurality ofchunks to the compressed data logical volume 402 where compressed datais stored and, when the compressed data logical volume 402 iscompressed, the page length of the chunk which is assigned to thecompression logical volume which is the copy source and the page lengthof the chunk which is assigned to the compression data logical volumewhich is the copy destination are the same length. As a result, when thelogical volume which stores the compressed data is copied, high-speedcopying is possible without the need for random-access reading,compressed data expansion, or reconstruction of the compressed LUmapping table, and so forth.

(10) Other Embodiments

Note that the present invention is not limited to the foregoingembodiment and encompasses various modifications. For example, althoughvarious programs, management tables, and bitmaps are recorded in theinvolatile memory 130, same may also be recorded in the HDD 111. Theforegoing embodiment is described in detail for the purpose of makingthe present invention easy to understand but is not limited tocomprising all the configurations described. Further, part of theconfiguration of a certain embodiment can be replaced with aconfiguration of another embodiment. Configurations of other embodimentscan also be added to the configuration of a certain embodiment.Moreover, other configurations can also be added to, deleted from orreplace part of the configuration of each embodiment.

Furthermore, part or all of each of the foregoing configurations,functions, processing units, and processing means and so on may also berealized by hardware by means of an integrated circuit design or thelike, for example. Further, each of the foregoing configurations andfunctions and the like may also by realized by software as a result of aprocessor interpreting and executing programs which implement therespective functions. Programs and information such as tables and filesfor realizing each of the functions can be placed in a recording devicesuch as a memory, HDD, or SSD (Solid State Drive) or the like or on arecording medium such as an IC card, an SD card, or a DVD.

Moreover, In addition, control lines and information lines which areconsidered necessary for the description are shown but not all thecontrol lines and information lines need necessarily be shown formanufacturing purposes. In reality, mutually coupling almost all theconfigurations may also be considered.

REFERENCE SIGNS LIST

-   -   101 Host    -   102 Management terminal    -   110 Storage apparatus    -   123 CPU    -   124 Main memory    -   125 Cache memory    -   130 Involatile memory    -   131 Management terminal communication program    -   132 Pool management program    -   133 I/O processing program    -   134 LU copy program    -   135 Compression/expansion program    -   136 Compressed LU mapping table    -   137 Unused area management bitmap    -   138 Chunk management table

The invention claimed is:
 1. A storage apparatus which is coupled via anetwork to a host which issues data I/O requests, the storage apparatuscomprising: a storage unit configured to store data which is read and/orwritten by the host; and a control unit which is configured to: providelogical volumes including a compressed data logical volume for the host,manage storage areas which are provided by the storage unit as a pool,wherein the pool is divided into a plurality of chunks having aplurality of pages, and each of the chunks is associated with at leastone of the logical volumes, wherein each of the chunks has a storageaddress; compress data which is written to the compressed data logicalvolume by the host, and allocate a page in a chunk which is associatedwith the compressed data logical volume to the compressed data logicalvolume, wherein, when making a copy of the compressed data logicalvolume, the control unit is further configured to: assign a chunk havingpages of the same size as the page in the chunk associated with thecompressed data logical volume to a copy destination logical volume, andcopy data of the compressed data logical volume in order of a storageaddress of the chunk associated with the compressed data logical volumewithout decompressing the data.
 2. The storage apparatus according toclaim 1, wherein the logical volume further includes an uncompressedlogical volume provided for the host, wherein a size of a page in achunk which is associated with the uncompressed logical volume isdifferent from the size of the page in the chunk associated with thecompressed logical volume.
 3. The storage apparatus according to claim1, wherein the control unit is configured to manage, in a mapping table,the storage address of each page in the chunk associated with a logicaladdress of the compressed data logical volume, and wherein the storageaddress of each page corresponds to an offset address in the chunk. 4.The storage apparatus according to claim 3, wherein the control unit isconfigured to employ the same mapping table for the compressed datalogical volume and the copy destination logical volume of the compresseddata logical volume.
 5. The storage apparatus according to claim 2,wherein the control unit is configured to: receive a request to changean attribute of the uncompressed logical volume to a compressed logicalvolume, read data stored in the chunk associated with the uncompressedlogical volume, compress the read data, and store the compressed readdata in the chunk associated with the compressed logical volume whoseattribute is changed to the compressed logical volume, wherein a size ofthe page in the chunk which is associated with the compressed logicalvolume is different from the size of the page in the chunk associatedwith the uncompressed logical volume.
 6. The storage apparatus accordingto claim 1, wherein, in a case where the compressed data logical volumeand the copy destination logical volume are in a pair state, the controlunit is configured to: receive a write request to the compressed datalogical volume from the host, read compressed data corresponding towrite data of the write request from the chunk associated with thecompressed logical volume to a cache memory, overwrite the readcompressed read data with the write data of the write request, copy theoverwritten data in the cache memory to a cache memory for thedestination logical volume, and store the overwritten data in the chunkassociated with the compressed logical volume and the destinationlogical volume.
 7. A method of managing data to be stored in a storageapparatus which is coupled via a network to a host which issues data I/Orequests, the method comprising: storing, in a storage unit, data whichis read and/or written by the host; providing, in a control unit, aplurality of logical volumes including a compressed data logical volumefor the host; managing storage areas which are provided by the storageunit as a pool, the pool being divided into a plurality of chunks havinga plurality of pages, and each of the chunks being associated with atleast one of the logical volumes and having a storage address;compressing data which is written to the compressed data logical volumeby the host, and allocating a page in a chunk which is associated withthe compressed data logical volume to the compressed data logicalvolume, wherein the method further comprises copying the compressed datalogical volume, and wherein copying the compressed data logical volumecomprises assigning a chunk having pages of the same size as the page inthe chunk associated with the compressed data logical volume to a copydestination logical volume, and copying data of the compressed datalogical volume in order of a storage address of the chunk associatedwith the compressed data logical volume without decompressing the data.8. The method of managing data according to claim 7, wherein the logicalvolume further includes an uncompressed logical volume provided for thehost, wherein a size of a page in a chunk which is associated with theuncompressed logical volume is different from the size of the page inthe chunk associated with the compressed logical volume.
 9. The methodof managing data according to claim 7, further comprising: managing, ina mapping table, the storage address of each page in the chunkassociated with a logical address of the compressed data logical volume,wherein the storage address of each page corresponds to an offsetaddress in the chunk.
 10. The method of managing data according to claim9, wherein the managing the storage address comprises employing the samemapping table for the compressed data logical volume and the copydestination logical volume of the compressed data logical volume. 11.The method of managing data according to claim 8, further comprising:receiving a request to change an attribute of the uncompressed logicalvolume to a compressed logical volume, reading data stored in the chunkassociated with the uncompressed logical volume, compressing the readdata, and storing the compressed read data in the chunk associated withthe compressed logical volume whose attribute is changed to thecompressed logical volume, wherein a size of the page in the chunk whichis associated with the compressed logical volume is different from thesize of the page in the chunk associated with the uncompressed logicalvolume.
 12. The method of managing data according to claim 7, wherein,in a case where the compressed data logical volume and the copydestination logical volume are in a pair state, the method furthercomprises: receiving a write request to the compressed data logicalvolume from the host, reading compressed data corresponding to writedata of the write request from the chunk associated with the compressedlogical volume to a cache memory, overwriting the read compressed readdata with the write data of the write request, copying the overwrittendata in the cache memory to a cache memory for the destination logicalvolume, and storing the overwritten data in the chunk associated withthe compressed logical volume and the destination logical volume.